1. Field of the Invention
The present invention relates to a float device such as ocean observation float device, which is called a “profiling float” used for an ocean monitoring system (which will be called Argo program below), and particularly to a technique capable of reducing the number of parts and adjusting a buoyant force with high accuracy.
2. Description of the Related Art
In order to address the environmental problems such as global warming, it is necessary to reveal environmental variation mechanisms in the global environment and to determine the total amount and the circulation of greenhouse gas. The Argo program is being promoted in order to address the problems. Under the Argo program a cylinder-shaped ocean observation float device having a length of 1 m which is called a “profiling float” is deployed from a ship, then automatically descends up to a depth (about 2000 m) in balance with a preset density of around water, and drifts for several days. When the power supply is turned on by an internal timer, the ocean observation float device comprising a float hull having a certain buoyancy is raised by a buoyant force adjustment mechanism.
The ocean observation float device is ascending while measuring water temperature and salinity. The ocean observation float device floating on the sea surface is powered off after transmitting the observation data from the sea surface via satellites, and is caused to descend by the buoyant force adjustment mechanism. The operation is repeated for several years.
The above buoyant force adjustment mechanism is configured as follows, for example. That is, FIG. 4 is an explanatory diagram schematically snowing a buoyant force adjustment mechanism 100 for adjusting a buoyant force of an ocean observation float device by carrying hydraulic oil between an external buoyant force adjustment bladder and an internal oil reservoir. The buoyant force adjustment mechanism 100 comprises an internal oil reservoir 110 for storing hydraulic oil therein, a plunger 120 and an external buoyant force adjustment bladder 130, which are connected via oil pipes 140, 141 and 142. The oil pipes 140, 141 and 142 are provided with a check valve 150, a check valve 151 and a valve 152, respectively.
In the buoyant force adjustment mechanism 100, when the hydraulic oil is carried from the internal oil reservoir 110 to the external buoyant force adjustment bladder 130, the plunger 120 is moved in the arrow α direction In FIG. 4 while the valve 152 is closed, and the hydraulic oil is taken from the internal oil reservoir 110 into the plunger 120. At this time, the hydraulic oil cannot be sucked from the external buoyant force adjustment bladder 130 by the operation of the check valve 151. Then, the plunger 120 is moved in the arrow β direction in FIG. 4 and the hydraulic oil is supplied from the plunger 120 to the external buoyant force adjustment bladder 130. At this time, the hydraulic oil does not return to the internal oil reservoir 110 because of the operation of the check valve 150. When the external buoyant force adjustment bladder 130 swells in this way, the ocean observation float device ascends.
On the other hand, when the ocean observation float device descends, the hydraulic oil is returned from the external buoyant force adjustment bladder 130 to the internal of reservoir 110. In this case, the valve 152 is opened so that the hydraulic oil is returned to the internal oil reservoir 110 by a contraction force of the external buoyant force adjustment bladder 130.